This invention relates to a pneumatic radial tire having an improved high-speed durability with its weight kept reasonably small and its capability of giving a driver a good ride in the car kept excellent.
In a pneumatic radial tire, at least two belt layers are buried between a carcass and a tread so that the cords in these belt layers cross each other, for the purpose of reinforcing the tread. There are some conventional radial tires for passenger cars in which one of at least two belt layers is folded back at its both widthwise end portions toward the equator of the tire so as to prevent the separation of the belt edges when the car travels at a high speed.
However, in these days in which a higher speed travel has been demanded, a conventional radial tire having the above-described structure is no longer suitable for a ultra-high speed travel of a car unless the width of the folded portions of a belt layer is increased, or it becomes necessary to provide one or a plurality of layers of belt covers so as to extend over the whole width of the belt layers to meet the speed requirement. Indeed, such modifications improved the high-speed durability of the tire, but at the cost of increased weight of the tire and decreased comfortableness of riding in the car.